1. Field of the Invention
The present invention relates to a combustion chamber of an engine.
2. Description of the Related Art
In a known two-stroke diesel engine, a masking wall is provided for masking a part of the valve opening between the valve seat and the intake valve and also masking a part of the valve opening between the valve seat and the exhaust valve when the valve lifts of the intake valve and the exhaust valve are small (U.S. Pat. No. 4,162,662). In this two-stroke diesel engine, fresh air is prevented from flowing into the combustion chamber from the part of the valve opening of the intake valve, masked by the masking wall, and burned gas is prevented from being discharged from the part of the valve opening of the exhaust valve, masked by the masking wall.
In a two-stroke engine disclosed in Japanese Patent Application No. 63-102659 which was assigned to the same assignee, a masking wall is provided for masking a part of the valve opening between the valve seat and the intake valve for the entire time for which the intake valve is open. In this two-stroke engine, fresh air or an air-fuel mixture is prevented from flowing into the combustion chamber from the part of the valve opening of the intake valve, masked by the masking wall for the entire time for which the intake valve is open.
In addition, in a known engine, built-up layers made of a metallic material which is different from that of the cylinder are formed on the peripheral portions of the openings of the intake port and the exhaust port. The valve seats of the intake valve and the exhaust valve are formed by machining the built-up layers (Japanese Unexamined Patent Publication No. 62-150014).
However, both the two-stroke diesel engine disclosed in the above-mentioned U.S. Pat. No. 4,162,662 and the two-stroke engine disclosed in the above-mentioned Japanese Patent Application No. 63-102659 have constructions where the valve seats of the intake valve and the exhaust valve are press-fitted into the annular grooves formed on the inner wall of the cylinder head. Nevertheless, where the valve seats are mounted on the inner wall of the cylinder head by the press-fitting, since the masking walls must be formed outwardly from, i.e., spaced from the outer periphery of the annular grooves to press-fit the valve seats of the intake valve and the exhaust valve into the annular grooves, large clearances are formed between the masking wall and the outer periphery of the intake valve and between he masking wall and the outer periphery of the exhaust valve. Consequently, even if the masking walls are arranged to mask the valve openings of the intake valve and the exhaust valve, fresh air, an air-fuel mixture, or burned gas flows through such clearances, and thus a problem occurs in that it is impossible to completely mask a part of the valve opening of the intake valve or a part of the valve opening of the exhaust valve by the masking wall.